1. Field of the Invention
The invention relates to fabrication methods for polynary chalcopyritic powders, and in particular to solvothermal synthesis methods for polynary chalcopyritic powders enhanced by microwave heating.
2. Description of the Related Art
Fabrication processes for forming a copper arsenide (indium) diselenide absorption thin film are chiefly divided into vacuum processes and non-vacuum processes. The vacuum processes include co-evaporation, and selenization, while the non-vacuum processes include spray pyrolysis, electro-deposition, and paste coating. With aspect to powder synthesis, high-energy mechanical alloying and solo-thermal methods are most popular.
The copper arsenide (indium) diselenide made from co-evaporation can be applied as an absorption layer of a thin-film solar cell reaching a maximum efficiency of approximately 19.5%. Cost of the co-evaporation equipment, however, is very expensive such that many research institutes are researching development of non-vacuum processes. Conventionally, the non-vacuum processes include thin film deposition and powder synthesis. Since the copper arsenide (indium) diselenide absorption layer is very sensitive to composition variations, thin film deposition of the copper arsenide (indium) diselenide is a great challenge. Thus, powder synthesis of the copper arsenide (indium) diselenide with a precisely controlled composition, is a mainstream non-vacuum process.
The main drawback of the conventional solution synthesis of the copper arsenide (indium) diselenide nano-scale powders is that it is time consuming. For example, Carmalt et al., discloses a method for synthesizing copper arsenide (indium) diselenide powders in 1998. Methylbenzene is applied as solvent, and solution consisting of copper chloride, indium chloride and sodium selenide is continuously heated 72 hours by refluxing. However, heating temperature has to reach 500° C. for a prolonged 24 hours to acquire a pure phase chalcopyritic structure. The equation for the chemical reaction is indicated as follows:2CuCl2+2InCl3+5Na2Se→2CuInSe2+10NaCl+Se.
Other solution methods can achieve a fast reaction. For example, Kyung Hoon Yoon et al., discloses a method for synthesizing copper arsenide (indium) diselenide powders in 2006. Cuprous iodide (CuI), indium triiodide (InI3), and gallium triiodide (GaI3) are solved in pyridine by a gel process and reacted with sodium selenide (NaSe) which is solved in methanol. Copper arsenide (indium) diselenide powders, therefore, can be synthesized within a short period of time. The pyridine, however, is dangerously poisonous limiting applications thereto.
FIG. 1 is a flow chart illustration a conventional synthesized method for chalcopyritic structure powders by a solvothermal method. First, copper chloride (CuCl2.2H2O), indium chloride (InCl3.4H2O), and Se power with molar ratio 1:1:2 are solved in ethylenediamine and are positioned in a Teflon autoclave (step S10). Subsequently, the Teflon autoclave is put into an oven heated thereupon at 180° C. for a prolonged 15 hours (step S20). Next, the Teflon autoclave is cooled to room temperature, and the ethylenediamine solution is washed with D. I. water and ethanol and filtered for depositions. The abovementioned process is repeated several times to remove byproducts (step S30). The ethylenediamine solution is baked in a vacuum oven at 60° C. for a prolonged 4 hours to acquire pure phase nano-scale chalcopyritic powders (step S40).
One of the drawbacks for the conventional solvothermal method is that it is time consuming. Moreover, pure phase chalcopyritic powders are difficult to acquire. Accordingly, a synthesis method with a shortened process and high production efficiency is needed for those having ordinary skill in the art, to efficiently produce pure phase nano-scale chalcopyritic structure powders.